This invention relates to an automobile speed control system, and in particular to an automobile speed control system which automatically serves to hold the running speed of an automobile at a fixed value.
Recently, automobiles or the like have been equipped with a speed control apparatus which automatically controls the automobiles to run at a specific target speed as preset on the speed control apparatus.
For such a speed control apparatus for an automobile, one as disclosed in Japanese Patent Application Laid-open No. 58-98636 has been conventionally used. Generally in this speed control apparatus, a setting operation for a target speed is done in a running state when a constant speed is desired, whereby the automobile is controlled to run at the set speed as its target speed. The actual running speed is compared with the target speed at all times, and the automobile's speed is controlled by the compared result so that when the former is lower than the latter, the output of the engine of the automobile is increased while when the former exceeds the latter, the output of the engine is decreased, thereby causing the former to approach the latter.
However, a disadvantage in such a conventional speed control apparatus for an automobile arises during varying road conditions, for example a road which is alternatively ascending and descending, since the deviation between the target speed and the running speed may become excessively large and a hunting operation may arise due to such a large deviation, resulting in an uncomfortable ride.
On the other hand, the U.S. Pat No. 4,202,424 issued to Sakakibara et al. on May 13, 1980 discloses an automobile speed control system wherein an error signal between the actual and desirable automobile speeds is derived to shift the throttle valve into a position at which both of the speeds are equal to each other while being fed back through an electrical first order lag circuit to a comparator for developing an error signal to stabilize the speed control operation of the system.